Sheet transporting cylinder, and corresponding transport device, printing press and use of said cylinder

ABSTRACT

A transporting cylinder ( 54 ) for a flat substrate, including a cylindrical base body ( 70 ) that has a cylindrical base body surface ( 74 ) having a first material and that has openings ( 82 ) leading out onto the cylindrical surface. 
     The transporting cylinder ( 54 ) includes a sleeve ( 72 ) arranged on the cylindrical surface ( 74 ), the covering element having a plurality of through-holes ( 92 ) aligned with at least some of the openings ( 82 ). The sleeve ( 72 ) has an outer covering surface ( 88 ) made from a second material. The outer surface ( 88 ) has a surface energy lower than the surface energy of the first material.

The present invention concerns a cylinder for transporting a flat substrate.

BACKGROUND

Devices for conveying printed products, such as sheets of paper, are known from the prior art. These conveying devices are for example used in offset printing machines to transport the printed sheets.

These conveying devices comprise hollow transport rollers having a transport surface in contact with the sheet to be transported.

In order to make the sheet adhere on the transport roller, the latter part includes recesses connected to a device for forming a vacuum.

However, the printed sheets lead to rapid wear of the transport surface, and result in marking the recesses on the printed sheet. This results in poor production quality.

SUMMARY OF THE INVENTION

The present invention aims to improve the quality of printed products that can be produced by the printing machine, with simple means.

The present invention provides a transporting cylinder of the indicated type, characterized in that it comprises a covering element arranged on the cylindrical base body surface, the covering element having a plurality of through-holes aligned with at least some of the openings, the covering element having an outer covering surface, the outer covering surface being made from a second material, different from the first material, and in that the outer covering surface has a surface energy lower than the surface energy of the first material.

The present invention provides a transporting cylinder including one or several of the following features:

-   -   the outer covering surface is made of an ink repelling material;     -   the second material comprises, and is preferably made of,         polytetrafluorethylene or silicone;     -   the through-holes are rounded at their junction with the outer         covering surface;     -   the through-holes have, in the non-stressed state of the         covering element, a diameter smaller than a diameter of the         openings;     -   the covering element comprises a first axial section provided         with holes and a second solid axial section, without holes, and         the second solid axial section covers an axial portion of the         base body provided with openings; and     -   the covering element is a cylindrical sleeve and the outer         covering surface is a surface of the sleeve.

The invention also concerns an assembly comprising a transporting cylinder as defined above, the covering element having a first thickness, and the assembly comprising a spare covering element, the spare covering element having a second thickness, different from the first thickness.

The invention also concerns a device for transporting a flat product, of the type including:

-   -   a transporting cylinder for the flat product;     -   a vacuum device adapted to create a vacuum;

wherein the transporting cylinder is a cylinder as defined above, and at least part of the plurality of openings is connected to the vacuum device.

According to one particular embodiment, the transporting device is a device for cutting a strip of sheets, it comprises a cutting cylinder, and the transporting cylinder is an impression cylinder of the cutting cylinder.

The invention also concerns a printing press, comprising a printing unit adapted to print on a strip of paper, and a transporting device of the aforementioned type.

The invention also concerns a use of a transporting cylinder of the aforementioned type, comprising the following successive steps:

-   -   transporting a predetermined quantity of paper using the         transporting cylinder,     -   removing the covering element from the base body, and     -   placing a non-worn covering element on the base body.

The invention also concerns the use of an assembly of the aforementioned type, comprising the following successive steps:

-   -   transporting a predetermined quantity of paper using the         transporting cylinder,     -   removing the covering element from the base body, and     -   adjusting the traction exerted on the paper by placing the spare         covering element on the base body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood upon reading the following description, provided solely as an example and done in reference to the appended drawings, in which:

FIG. 1 is a diagrammatic side view of a printing machine according to the invention;

FIG. 2 is a view corresponding to the view of FIG. 1, of an alternative printing machine according to the invention;

FIG. 3 is a diagrammatic view of the cutting and stacking device of the press of FIGS. 1 and 2;

FIG. 4 is an axial cross-sectional view of the impression cylinder; and

FIG. 5 is an enlarged view of detail V of FIG. 4.

DETAILED DESCRIPTION

FIG. 1 shows a rotary printing machine according to the invention, designated by general reference 2.

The printing machine 2 comprises an unwinder 4, four printing units 6, a traction device 8, and a cutting and stacking device 10. The printing machine 2 also comprises a strip capture device 14 and a chalking device 16.

The printing machine 2 could comprise any number of printing units 6, in theory, from one to n.

The unwinder 4 is adapted to unwind a continuous strip to be printed 18.

The strip to be printed 18 is a strip of coated paper. Coated paper is paper that comprises a coating layer, for example made of kaolin or chalk, improving the mechanical or optical properties of the paper. This paper makes it possible to obtain a high quality printed product. Alternatively, it is possible for the strip to be printed to be a strip of uncoated paper.

The printing machine 2 defines a printing path of the strip 18 between the unwinder 4, through the printing units 6, the strip capture device 14, the chalking device 16, and the traction device 8, up to the cutting and stacking device 10.

Each printing unit 6 includes an inking roller device 20 that is provided with an ink tank 22 comprising ink 24 provided for printing on a strip of paper 18. The ink 24 used in the context of the invention will be explained below. Each inking roller device 20 also comprises an ink transfer roll 26 to transfer the ink 24 to the print rolls 28 (see below).

The printing units 6 comprise these print rolls 28, which are adapted to print on a strip of paper 18.

The cutting and stacking device 10 is adapted to cut the strip to be printed 18 into individual sheets 30 and to produce a stack of cut individual sheets.

The traction device 8 is situated downstream of the printing unit 6 farthest downstream and upstream of the cutting and stacking device 10. This traction device 8 is adapted to apply a determined mechanical traction on the strip 18 coming out of the printing unit 6 farthest downstream.

As shown in FIG. 1, the printing machine 2 is adapted to transport the printed strip 18 in free suspension and in ambient air over the entire path between the printing unit 6 farthest downstream and the traction device 8, possibly with the exception of the strip capture device 14 and the chalking device 16. Moreover, the printing machine 2 is also adapted to transport the printed strip 18 in ambient air over the entire path between the traction device 8 and the cutting and stacking device 10. Thus, the printing machine 2 of FIG. 1 does not include a dryer and has a small bulk.

The printing machine 2 according to the alternative shown in FIG. 2 differs from the printing machine 2 shown in FIG. 1 by the fact that between the strip capture device 14 and the traction device 8 is an infrared dryer 32 through which the printed strip 18 is conveyed. The infrared dryer 32 can be replaced by another heat drying device of the strip, such as a hot air dryer. The dryer 32 has reduced dimensions in relation to the dryers of the prior art.

The strip capture device 14 is adapted to detect a break in the paper strip 18 and the catch the free end of the paper strip 18 in that case. To that end, the strip capture device 14 includes suitable capture elements 34. Alternatively, the strip capture device 14 is omitted.

The chalking device 16 is adapted to deposit anti-spotting powder on each of the faces of the printed strip 18. It can deposit anti-spotting powder on one or both of the faces of the printed strip. To that end, the chalking device 16 includes a tank 36 containing powder 38 and a chalking head 40 connected to the ink tank 36 by a duct 42, for each of the faces of the paper strip 18.

The chalking device 16 is adapted to apply anti-spotting powder on the paper strip 18 continuously, preferably continuously without interruption over a length corresponding to at least twice the printing length.

The powder 38 used to chalk the strip is preferably a vegetable powder, for example corn-based, or a mineral powder.

The traction device 8, connected to the other units of the press, makes it possible to print a strip of paper and receive it in the cutting and stacking device 10, without drying the strip of paper 12 and through evaporation of the ink solvents.

The image is printed by the ink 24 contained in the ink tank 22. Advantageously, the ink 24 is a siccative ink, or a waterless ink, or a bi-component ink. Drying of siccative inks is a combination of a first phenomenon called “penetration in the medium” and a second phenomenon called “oxido-polymerization of varnishes made up of oils and resins.”

Waterless inks are used with specific printing plates making it possible to define non-printing areas without using the traditional lithographic method based on the rejection of greasy ink by a previously moistened hydrophilic surface. The use of these inks can be considered in the same way as the traditional siccative inks previously seen and makes it possible to do away with a dryer, or to design it so that it is less bulky.

Heat-set inks, on the other hand, dry through evaporation of the mineral solvents mixed in with the resin. UV inks dry by polymerization of the resin under the effect of ultraviolet radiation.

FIG. 3 diagrammatically illustrates the cutting and stacking device 10.

The cutting and stacking device 10 includes two entering rolls 50, a cutting cylinder 52, an impression cylinder 54, a transfer roll 56, and a braking roll 58.

The cutting and stacking device 10 includes a fixed structure S or frame.

The cutting device 10 defines a path T of the paper strip 18 and the sheets 30 extending from the entrance of the device successively on the entering rolls 50, the impression cylinder 54, the transfer roll 56, the braking roll 58 up to a stack 31 of individual sheets 30.

The entrance rolls 50 are arranged on the path T upstream of the cutting cylinder 52 and the impression cylinder 54.

The two entrance rolls 50 are able to rotate around an axis A and B in relation to the fixed structure S. Each of the entrance rolls 50 includes a jacket 60 having through-holes 62.

The cutting cylinder 52 rotates around an axis C and includes a blade 66. The blade 66 cooperates with impression blocks 68 arranged on the impression cylinder 54.

The impression cylinder 54 includes a cylindrical base body 70 and a cylindrical sleeve 72.

The base body 70 is a cylinder with a hollow circular section and defines an outer cylindrical surface 74 and an inner cylindrical surface 76 of the base body. The base body 70 is made of a first material, which is preferably hard, such as steel or ceramic. This first material has a given surface energy.

The impression cylinder 54 includes a flange 78 to which the base body 70 is fixed (cf. FIG. 4). This flange 78 is housed in a roll 80. Thus, the base body 70, the sleeve 72 and the flange 78 are mounted able to rotate in relation to the frame S around the axis of rotation D.

The base body 70 includes through recesses 82, extending from the inner surface 76 to the outer surface 74 and leading out onto this outer surface 74. In this case, these recesses 82 are through holes, extending radially in relation to the axis D. The recesses 82 have a diameter D1.

The base body 70 includes a first axial portion 84 provided with recesses 82 and at least one second axial portion 86 without recesses 82. The second axial portion 86 has a solid wall. In this case, the first axial portion 84 is situated at the axial center of the base body 70 and the base body 70 includes two second axial portions 86 situated on either side of the first axial portion 84.

The sleeve 72 is cylindrical and includes an outer 88 and inner 90 cylindrical sleeve surface. The sleeve is arranged on the outer surface 74 of the base body 70.

The sleeve 72 includes a plurality of through-holes 92 extending from the outer surface 88 to the inner surface 90.

A multitude of these holes 92 is aligned each time with one of the recesses 82. Preferably, each of the holes 92 is aligned with one of the recesses 82. The holes 92 have, in the unstressed state of the sleeve 72, i.e. when the recesses 82 are subject to ambient pressure, a second diameter D2, which is smaller than the first diameter D1 of the recesses.

The sleeve 72 is made of a second material, which has a surface energy lower than the surface energy of the first material of the base body 70 and which rejects the ink used to print on the strip 18. The material of the sleeve 72 is also more flexible than the material of the base body 70. Preferably, the sleeve 72 comprises, or is made up of, polytetrafluorethylene (PTFE) or silicone. At least the outer surface 88 of the sleeve 72 has the properties of the second material. The sleeve 72 has a thickness DM.

The sleeve 72 comprises a first axial section 100 provided with holes 92. The sleeve 72 also comprises at least one second axial section 102 without holes 92 and comprising a solid wall over its entire circumference. In this case, the sleeve 72 comprises two second axial sections 102 situated on either side of the first axial section 100.

Each second axial section 102 is arranged on the first axial portion 84 of the base body 70 and thus covers a portion of the recesses 82. Preferably, the second axial sections 102 cover the recesses 82 over the entire axial width that is not covered by the strip 18 or by a sheet 30.

Preferably, the first section 100 has an axial length 1 identical to the width L of the paper strip 18 minus the side lay R. Thus, the sleeve 72 makes it possible to adapt the counter-cut cylinder 54 to the width L of the strip of paper 18.

Preferably, the holes 92 are rounded at their junction with the outer surface 88 of the sleeve 72. Thus, the marking of the sheets 30 or strip 18 is reduced.

The counter-cut cylinder 54 also includes a cylindrical inner wall 110 and two sealing gaskets 112 fixed to the structure S. The wall 110, the sealing gaskets 112 and the base body 70 define a vacuum chamber 114 exclusively connected on a part of the circumference to the recesses 82. In this case, the vacuum chamber 114 extends over an angle α, which is identical to the contact angle of the paper strip 18 on the cylinder 54. The angle α is for example between 90° and 180° and is in any case smaller than 360°.

The counter-cut cylinder 54 also defines an ambient chamber 116, subject to ambient pressure. The ambient chamber 116 extends over an angle β around the axis D, β being 360°-α.

The cutting device 10 also includes a vacuum device 120 connected to the vacuum chamber 114 and adapted to create an under-pressure in said chamber 114. The vacuum device 120 is also connected to the entrance rolls 50 and the transfer 56 and braking 58 rolls in order to create an under-pressure on part of the circumference of said rolls.

The invention operates as follows.

The vacuum device 120 creates an under-pressure in the vacuum chamber 114. Under the effect of the pressure difference between the vacuum chamber 114 and the environment, the parts of the sleeve 72 surrounding the holes 92 are aspirated in the recesses 82 (Cf. FIG. 5) and are elastically deformed. This is made possible owing to the flexibility of the sleeve 72.

The strip 18 is printed by the printing units 6 and is conveyed in the cutting device 10. The paper strip 18 is conveyed by the entrance rolls 50 toward the cutting cylinder 52 and impression cylinder 54.

The paper strip 18 is cut by the blade 66 into sheets 30.

The portion of the paper surrounding the impression cylinder 54 is aspirated by the openings 82 and the holes 92 and retains the paper on the outer surface 88 of the sleeve 72.

Owing to the properties of the outer surface 88 of the sleeve 72, the ink does not adhere to that surface. Furthermore, owing to the rounded parts of the outer surface 88 of the sleeve, the paper is not plastically deformed at the locations of the holes 92.

When the sleeve 72 is worn, it is exchanged for another sleeve 72 that is not worn. Thus, the cylinder according to the invention makes it possible to save material and is economical in terms of upkeep.

The invention was explained according to the example of a counter-cut cylinder. The aforementioned features can also be applied similarly to any transport cylinder adapted to transport paper.

The aforementioned features can also be applied similarly to the transport of a flat substrate that is not paper.

According to one alternative, the base body 70 is not covered with a closed sleeve 72, but with another covering element, such as one or several flat plates. Aside from the different shape, these flat strips have the same features as the aforementioned sleeve 72. The flat strips are stuck on the base body 70.

The sleeves can also be used to adjust the strain exerted on the paper strip 18. To that end, the sleeve 72 having the thickness DM is changed out for a spare sleeve having a thickness different from the thickness DM. 

1-13. (canceled)
 14. A transporting cylinder for a flat substrate comprising: a cylindrical base body having a cylindrical surface having a first material having a first material surface energy and a plurality of openings leading out onto the cylindrical surface; a covering element arranged on the cylindrical base body surface, the covering element having a plurality of through-holes aligned with at least some of the openings, the covering element having an outer covering surface, the outer covering surface being made from a second material, different from the first material, and in that the outer covering surface has a surface energy lower than the first material surface energy.
 15. The transporting cylinder according to claim 14 wherein the outer covering surface is made of an ink repelling material.
 16. The transporting cylinder according to claim 14 wherein the second material comprises polytetrafluorethylene or silicone.
 17. The transporting cylinder according to claim 14 wherein the through-holes are rounded at their junction with the outer covering surface.
 18. The transporting cylinder according to claim 14 wherein the through-holes have, in the non-stressed state of the covering element, a diameter smaller than a diameter of the openings.
 19. The transporting cylinder according to claim 14 wherein the covering element comprises a first axial section provided with the through-holes and a second solid axial section, without the through-holes or other through-holes, and the second solid axial section covers an axial portion of the base body provided with openings.
 20. The transporting cylinder according to claim 14 wherein the covering element is a cylindrical sleeve and the outer covering surface is a surface of the sleeve.
 21. An assembly comprising a transporting cylinder according to claim 14, the covering element having a first thickness, and further comprising a spare covering element, the spare covering element having a second thickness, different from the first thickness.
 22. A device for transporting a flat product comprising: a transporting cylinder according to claim 14 for the flat product; and a vacuum device adapted to create a vacuum; at least part of the plurality of openings being connected to the vacuum device.
 23. The transporting device according to claim 22 wherein the transporting device is a device for cutting a strip into sheets, and further comprises a cutting cylinder, the transporting cylinder being an impression cylinder of the cutting cylinder.
 24. A printing press comprising: a printing unit adapted to print on a strip of paper; and a transporting device according to claim
 22. 25. A method for operating a transporting cylinder according to claim 14 comprising the following successive steps: transporting a predetermined quantity of paper using the transporting cylinder; removing the covering element from the base body; and placing a non-worn covering element on the base body.
 26. A method for operating an assembly according to claim 21 comprising the following successive steps: transporting a predetermined quantity of paper using the transporting cylinder; removing the covering element from the base body; and adjusting a traction exerted on the paper by placing the spare covering element on the base body. 